1. Field of the Invention
The present invention relates to a film formation apparatus for a semiconductor process for forming a thin film made of, e.g., SiO2 on a target object, such as a semiconductor wafer, and a method for using the same, and particularly to a technique for inhibiting metal contamination inside the film formation apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target object, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target object.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, there is used a film formation step for forming a thin film made of, e.g., SiO2 on a semiconductor wafer, such as a silicon wafer. In the film formation step, a vertical heat processing apparatus of the batch type may be used to perform film formation by chemical vapor deposition (CVD) on a plurality of semiconductor wafers together at a time.
Owing to the demands for increased miniaturization and integration of semiconductor devices, thin films made of, e.g., SiO2 are required to have higher quality. For example, Jpn. Pat. Appln. KOKAI Publication No. 2003-7700 discloses a technique for realizing a thin film of high quality. According to this technique, an ALD (atomic layer deposition) or MLD (molecular layer deposition) method is used to form an SiO2 film by alternately supplying a source gas of a thin film, such as an Si source gas, and an oxidizing agent to repeat lamination of films of an atomic layer level or molecular layer level.
Further, in manufacturing lines, a cleaning process using a cleaning gas is periodically performed to remove extraneous thin film components deposited inside a process container, so as to stably form a thin film of high quality.
On the other hand, Pat. Appln. KOKAI Publications No. 9-246256, No. 2002-313740, No. 2003-188159, and No. 9-171968 disclose techniques for forming a pre-coating inside a process container.
In recent years, thin films made of, e.g., SiO2 have being increasingly required to address higher quality. One of the key factors that affect the characteristics of thin films is metal contamination to thin films. A contaminant source of metal contamination is a metal slipped into a process container.
Although a cleaning process is periodically performed inside the process container, a trace quantity of metal components may be mixed in a cleaning gas to be used for this cleaning process.
If metal components are mixed in the cleaning gas, a trace quantity of metal components is left in the process container after the cleaning process. Where residual metal components are very small in quantity and metal components scattered inside the process container fall within an allowable quantity range, they are harmless. However, the quantity of scattered metal components has been required to fall within a narrower allowable range year by year.
In the future, as regards a process container periodically cleaned by the conventional technique, if the allowable range becomes very narrow, it may be unacceptable to return the process container to the original line or it may be necessary to give up reuse of the process container.